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re: design question
9 feb 2006
wrote:
>harry chickpea wrote:
>
>> nick's idea of having a panel under an inch of water seems like a
>> solution to the heat build-up, as long as the water can be circulated
>> off and kept cool over the panel. one of the benefits of solar is the
>> "install it and forget it" aspect. a system like this might be fine
>> for a huge installation with a dedicated staff, but for home use, the
>> system will eventually run dry of water or not be maintained (due to
>> vacations - illness - job duties - laziness), and fail.
i don't see that as inevitable. no moreso than other draindown systems.
>for more widespread use rather than experimental, you'd have a ballcock
>that tops the water up, a small deioniser (low feed rate needed) and
>plastics that would survive long term. so no maintenance.
why deionize?
>the plastic cover of the unit can be light scattering to give good
>evenness of illumination, if necessary, with some loss...
i measured a 6% intensity loss with an inch of water and two layers of
0.006 inch 5 cents/ft^2 cloudy greenhouse polyethylene film duct with
a 4-year guarantee. an approximate linear parabolic reflector with 2 or 3
flat planes can help avoid hot spots.
>finally, in the event of pump failure, the panels are protected by boiling.
under 2-3 suns, they might be ok for a month or two dry.
>not sure what the metallisation on the panel would think of hot
>deionised water, maybe the panel would need gold flashing.
the film duct would sit on top of the panel with water between the films
and no water touching the panel face.
nick
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